Understanding Uterine Activity

Power and Passenger: Understanding Uterine Activity

Michelle Flowers RNC-OB Emily Hamilton MDCM

Michelle Flowers serves as a PeriGen Program Manager & Clinical Consultant. Her 20+ year career also includes experience as a Clinical Quality Coordinator, Educator for obstetric services, and L&D charge nurse.

Her more recent experience has focused on designing and executing OB documentation workflows and training programs. Her education credentials have included AWHONN Intermediate/Advanced Fetal Monitoring Instructor, ICEA Approved Trainer and Certified Childbirth Educator and AAP NRP Instructor. Featuring Emily Hamilton, MDCM Senior Vice President of Clinical Research

An experienced obstetrician, Dr. Hamilton is currently an Adjunct Professor of Obstetrics and Gynecology at McGill University, as well as leading PeriGen’s clinical research team. Dr. Hamilton is the inventor of the PeriCALM advanced fetal monitoring system, holding 32 US and international patents for her research work. She is an internationally-known clinical thought leader on the use of technology to improve obstetric outcomes. She presents her research regularly at obstetric conferences and in peer-reviewed journals. Objectives

1. Review definitions related to uterine activity

2. Review etiology and physiology of uterine tachysystole

3. Analyze impact of UT on the fetal heart rate Uterine Contractions Quantified as the number of contractions in 10 minutes averaged over 30 minutes.

• Uterine activity terminology used to assess and describe contractions: o Frequency – Beginning of contraction to beginning of next one o Duration – Length of contraction from beginning to end – Measured in seconds o Intensity – Strength of contraction – Assessed via palpation or mmHg (Montevideo units) o Resting Tone – Intrauterine pressure when uterus is not contracting – Assessed via palpation or mmHg Uterine Palpaon Palpation of uterine contractions is one of the key components of labor assessment.

Uterus Feels Like Contracon Intensity

Easily Indented Tip of Nose Mild

Slightly indented Chin Moderate

Cannot indent Forehead Strong Contractions

• Generate intrauterine pressure • Cause retraction, effacement and dilation of the cervix • Facilitate descent and birth of the fetus • Affect maternal blood flow through the myometrium • Normal contraction pattern – 5 Contractions or less in 10 minutes Resting Tone • Measured by palpation or IUPC • Normal – Assists in maintaining adequate fetal oxygenation • Hypertonus (elevated resting tone) – Palpation: uterus that doesn’t return to soft – IUPC: >20-25 mmHg Montevideo Units

• Two methods of measurement

• Measured in 10 minute segments – Measure peak intensity, or amplitude, in mmHg for each contraction and add together – Subtract baseline uterine tone from peak contraction pressure for each contraction and add together Other Contraction Measurements

Quantaon of uterine acvity in 100 primiparous paents. Miller FC, Yeh SY, Schifrin BS, Paul RH, Hon EH. Am J Obstet Gynecol. 1976 Feb 15;124(4):398-405. Physiology

Contractions

• The uterine muscle is composed of upper and lower uterine segments – Upper segment: active and contains pacemaker sites – Lower segment: passive zone

• At the start of labor, changing levels of various hormones cause myometrial cells to be more excitable. – (corticotrophin–releasing hormone, progesterone, estrogen, prostaglandin and oxytocin)

• Myometrium advances from a quiet to an active state.

• Contractions result when there is coordinated propagation of myometrial contraction usually beginning in the fundus

Contractions Intramyometrial Pressure Effect on Blood Flow Fleisher 1987 Brar 1988 Janbu 1987

• Maternal flow reduced

• Directly related to pressure • Spiral arteries compressed when pressures >35-60 mmHg

Compensatory Mechanisms

Healthy fetus has twice the reserve required to navigate the birth process. Redistribute • Extrinsic factors impacting FHR Patterns: blood ﬂow – Maternal Influences – Utero-placental perfusion – Umbilical circulation Reduce Fetal – Amniotic fluid characteristics O2 need reserves • Intrinsic factors impacting FHR Patterns: – Placental transfer capacity – Fetal adaptive compensatory mechanisms Increase

O2 extracon Uterine Tachysystole

Uterine Tachysystole

> 5 contractions per 10 minutes averaged over 30 minutes

Mathematical equivalent: >15 contractions in 30 minutes Causes of Tachysystole

• Known complication of induction/augmentation • Spontaneous – Intrauterine infection • “Irritation” of the myometrium by bacterial toxins – Placental abruption • Cocaine use • Unknown etiology

Physiology

Uterine Tachysystole

tc O2 Repeated 1 min Cord Occlusion Bennet L, Westgate JA, Liu YC, Wassink G, Gunn AJ. J Appl Physiol (1985). 2005

5 mins 2.5 min

First 30 min

Mid 30 min

Last 30 min

pH 7.34 stable… pH 7.25 7.14 6.92 BD 1.3 stable … BD 3.3 13.6 19.2 Fetal Experience

1. Amount of oxygen available correlated with contraction strength, duration and intercontraction interval.

2. Reperfusion time important to restore oxygen levels in the intervillous space before next contraction begins Incidence of UT UT lasting >1hr 4.2%

Clinical associaons with uterine tachysystole. Smith S, Zacharias J, Lucas V, Warrick PA, Hamilton EF. J Matern Fetal Neonatal Med. 2014 May;27(7):709-13 % DEP low even with UT >60min DEP = Neonatal Depression Umbilical artery BD ≥ 10 mmol/L or 5 minute Apgar ≤ 6

% UT: Higher with Oxytocin % DEP: low and similar % DEP in UT: low and similar More Decelerations Greater Exposure to UT

High uterine contracon rates in births with normal and abnormal umbilical artery gases. Hamilton E, Warrick P, Knox E, O'Keeﬀe D, Garite T. J Matern Fetal Neonatal Med. 2012 Nov;25(11):2302-7. Higher rate of #deceleration/#contractions HIE babies highest ratio Clinical Summary 1. UT is common (usual range ~11-26%)

2. How a baby responds to UT depends upon the balance between contraction-related decreases in perfusion and compensatory capacity of baby

3. Compensatory capacity is finite

4. Red flag: Deceleration response to any level of contractions

5. Red flag: What is causing the UT? Impact of UT on the Fetal Heart Rate Case Presentations

NVD pH 7.35 BD 0.6 Apgar 8/9 3800g 4663 Compensation capacity Is Finite

4 hrs before birth 9363 G3P0 40 3/7 wks

NVD pH 7.04 BD 13.3 Apgar 8/9 4100g 9363 G3P1 39 3/7 wks

NVD ph 7.05 BD 16.2 Apgar 8/9 3500g 6236 G1P0 39 0/7 wks

NVD pH 6.6 BD 27 Apgar 0/0 3300g 101018 Medicolegal Perspective

45% of brain injuries - Excessive use of contraction stimulating drugs Clark SL, et al Obstet Gynecol. 2008 Dec;112(6):1279-1283.

71% of births with severe asphyxia seeking legal action - incautious use of oxytocin Berglund S, et al . BJOG. 2008 Feb;115(3):316-323

47% of babies born with metabolic acidosis have oxytocin misuse Jonsson M, et al BJOG. 2009 Oct;116(11):1453-60.

>70% of closed legal claims with oxytocin use showed a failure to appreciate and act on severity of EFM abnormalities. 75% resulted in a settlement. CMPA Perspective, March 2014

UT in perspective

28,486 >34 wks, vaginal births 1994-2004 roune with umbilical artery gases

161 Severe metabolic acidosis UA pH <7.05 and BD ≥12 mmol/L

Excluded Elecve CS Catastrophic OB events (abrupon, cord prolapse, ecalmpsia)

UT => 6/10 x 20 minutes

Jonsson M, et al BJOG. 2009 Oct;116(11):1453-60. Metabolic Acidosis

Oxytocin misuse 47%

no oxytocin misuse 53% Metabolic Acidosis

UT and Oxytocin misuse Oxytocin misuse without UT 19% 28%

UT without Oxytocin Misuse

UT and Oxytocin misuse 19% Oxytocin misuse without UT 28%

UT without Oxytocin misuse 7%

46% UT Normal

UT without Oxytocin UT and Oxytocin misuse misuse 3.2% 3.7%

Oxytocin misuse without UT 10.0% Conclusions: Uterine Tachysystole

1. Fetal tolerance demonstrated by changes in FHR

2. Uterine tachysystole and/or failure to intervene for abnormal FHR is very common in OB litigation

3. Avoid it, Fix it, Can’t defend it! References

Ahmed AI, Zhu L, Aldhaheri S, Sakr S, Minkoﬀ H, Haberman S.Uterine tachysystole in spontaneous labor at term. J Matern Fetal Neonatal Med. 2016 Oct;29(20):3335-9

Aldrich CJ, D'Antona D, Spencer JA, Delpy DT, Reynolds EO, Wya JS. Fetal heart rate changes and cerebral oxygenaon measured by near-infrared spectroscopy during the ﬁrst stage of labour. Eur J Obstet Gynecol Reprod Biol. 1996 Feb;64(2):189-95.

Bakker PC, Kurver PH, Kuik DJ, Van Geijn HP. Elevated uterine acvity increases the risk of fetal acidosis at birth. Am J Obstet Gynecol. 2007 Apr;196(4):313.e1-6.

Bennet L, Westgate JA, Liu YC, Wassink G, Gunn AJ. Fetal acidosis and hypotension during repeated umbilical cord occlusions are associated with enhanced chemoreﬂex responses in near-term fetal sheep. J Appl Physiol (1985). 2005 Oct;99(4):1477-82.

Berglund S, Grunewald C, Peersson H, Cnangius S. Severe asphyxia due to delivery-related malpracce in Sweden 1990-2005. BJOG. 2008 Feb;115(3):316-23.

Brar HS, Pla LD, DeVore GR, Horenstein J, Medearis AL. Qualitave assessment of maternal uterine and fetal umbilical artery blood ﬂow and resistance in laboring paents by Doppler velocimetry. Am J Obstet Gynecol. 1988 Apr;158(4):952-6.

Clark SL, Belfort MA, Dildy GA, Meyers JA. Reducing obstetric ligaon through alteraons in pracce paerns. Obstet Gynecol. 2008 Dec;112(6):1279-83.

Managing the Risks of Labour Inducon. CMPA Perspecve March 2014 References Miller FC, Yeh SY, Schifrin BS, Paul RH, Hon EH. Quantaon of uterine acvity in 100 primiparous paents. Am J Obstet Gynecol. 1976 Feb 15;124(4):398-405.

Fleischer A, Anyaegbunam AA, Schulman H, Farmakides G, Randolph G. Uterine and umbilical artery velocimetry during normal labor. Am J Obstet Gynecol. 1987 Jul;157(1):40-3.

Hamilton E, Warrick P, Knox E, O'Keeﬀe D, Garite T. High uterine contracon rates in births with normal and abnormal umbilical artery gases. J Matern Fetal Neonatal Med. 2012 Nov;25(11):2302-7.

Janbu T, Nesheim BI. Uterine artery blood velocies during contracons in pregnancy and labour related to intrauterine pressure. Br J Obstet Gynaecol. 1987 Dec; 94(12):1150-5.

Jonsson M, Nordén-Lindeberg S, Ostlund I, Hanson U. Metabolic acidosis at birth and subopmal care--illustraon of the gap between knowledge and clinical pracce. BJOG. 2009 Oct;116(11):1453-60.

Klink F, Grosspietzsch R, Klitzing LV, Oberheuser F. Uterine contracon intervals and transcutaneous levels of fetal oxygen pressure. Obstet Gynecol. 1981 Apr; 57(4):437-40. Kunz MK, Lous RJ, Nichols AA. Incidence of uterine tachysystole in women induced with oxytocin.J Obstet Gynecol Neonatal Nurs. 2013 Jan-Feb;42(1):12-8.

Simpson KR, James DC. Eﬀects of oxytocin-induced uterine hypersmulaon during labor on fetal oxygen status and fetal heart rate paerns. Am J Obstet Gynecol. 2008 Jul;199(1):34.e1-5.

Smith S, Zacharias J, Lucas V, Warrick PA, Hamilton EF. Clinical associaons with uterine tachysystole. J Matern Fetal Neonatal Med. 2014 May;27(7):709-13.